Take a SMART approach with compressed air leaks
Measure the problem, then set out on a repair journey
With increasing market expectations associated with energy efficiency and sustainability, most corporate business reviews include a summary of energy conservation projects and performance. When the decision is made to identify additional savings opportunities, fixing compressed air leaks is flagged as an opportunity to deliver savings quickly with minimal investment.
The desire to eliminate air leaks is echoed in discussions with customer focus groups and market research projects that seek to identify unmet needs of the industrial consumer. If it is generally accepted that compressed air leaks are a waste of money and easily repaired, why do they still exist?
As an organization with dedicated engineering resources focused on the assessment of compressed air systems to help customers improve efficiency, reliability and productivity, compressed air leaks are a routine topic of discussion among assessment engineers and compressed air users. Working with customers in North America, Ingersoll Rand developed a new leak assessment service-offering designed to help industrial customers manage air leaks more effectively.
As part of an ongoing effort to iteratively advance the efficiency and effectiveness of our leak assessment program, data from every recorded leak is collected and compiled in a central database. After collecting data from several hundred leak assessments, an analysis of thousands of recorded leaks identified trends and opportunities in the battle against compressed air leaks. These results are segmented into two areas—recorded leaks and the process of leak repair.
Identifying common leak locations
The data analysis revealed the majority of leaks—by volume and frequency—occur at the point of use, as illustrated in the Pareto chart (Fig. 1).
As shown in Fig. 1, the filter-regulator-lubricator (FRL) is the largest culprit of compressed air leaks, closely followed by the threaded joints along pipe drops and connections to pneumatic equipment. The point-of-use valves used to control actuation of single or multiple pneumatic devices is a close third.
On average, these three leak categories represent over 80% of the leaks identified in an industrial facility. The quick-disconnect type fittings, push-lock tube fittings, and hose/tube leaks are considered by many to be the most common components prone to leaks. They are identified as unique leak types segmented in the data. Contrary to common belief, these three applications combined represent only 16% of all identified leaks.
It is important to note that the analysis is based on data recorded and observed during leak assessments. The data does not differentiate between recurring leaks that are repaired frequently from a leak that has grown over time. Any application located very close to an operator has an increased probability of being identified and repaired. Therefore, the recorded data suggests that FRLs, control valves, and point-of-use threaded joints represent the largest source of leak repair opportunities that are not addressed.
Technicians use ultrasonic leak detection equipment to estimate leak volumes during assessments. To deliver consistent results, technicians train to use a standard process and tools. Technicians record the pressure at each location and utilize it to calculate leak volume with improved accuracy over more common methods that assume a constant pressure for all locations.
The data was compiled and summarized graphically in Figs. 2-4 by leak category, and then segmented according to leak volume and weighted frequency of occurrence.
According to the recorded data in Figs. 2-4, the average leak volume is 3 scfm for all leak categories. This implies there is no advantage to targeting one type of leak in hopes of delivering improved results relative to the number of leaks repaired. The number of leaks less than 1 scfm is very low, but this is influenced by the leak assessment process.
The cost to repair a small leak can exceed the savings potential beyond a site-specific financial threshold. Consequently, the majority of customers chose to not record these smaller leaks during the leak assessment. Another issue is being able to physically detect the leak. When a leak is less than 1 scfm, it is difficult for maintenance personnel to feel the leak and isolate the area that needs repair. There is no value in identifying and tagging leaks that will not be repaired.
Prioritizing leak repairs
To be efficient, leaks scheduled for repair should be prioritized by measured volume and ease of repair. This prioritization delivers the best return on time and effort. Referencing Figs. 2-4, the number of leaks larger than 6 scfm for all categories is very low, but this can be attributed to two influences: larger leaks are more audible, increasing awareness and accountability to repair the obvious energy waste; and as a leak increases in volume, so does its potential to negatively influence the application. As a result, many larger leaks are repaired to correct a performance issue, not to deliver energy savings.
Pareto law, often referred to as the 80/20 rule, is frequently quoted in regard to compressed air leaks. The assumption states that 80% of the total volume of air being wasted through leaks can be eliminated by repairing 20% of the identified leaks. The recorded data suggests that leaks do not adhere to this assumption.
To provide a simple prioritized summary of leaks from each assessment, recorded leaks are sorted by volume and summarized graphically using a Pareto chart. The data compiled by individual leak assessment and total recorded leaks for all assessments consistently follow an 80/70 relationship, where 80% of the total volume can be eliminated by repairing 70% of the leaks. This is very different from the 80/20 assumption that many follow.
As the summary of leak categories in Fig. 1 illustrates, almost half of all leaks could be reduced by implementing an FRL maintenance program. Considering most facilities use standard FRL models and sizes across an entire facility, a maintenance technician equipped with several repair kits and replacement filter elements could easily fix a large number of leaks while simultaneously minimizing pressure variance and losses at each FRL station. This can be accomplished by segmenting FRLs by location or application, then scheduling annual filter replacements and leak inspections. Valves and threaded joints adjacent to the FRL should be included as part of the annual FRL preventive maintenance.
Using a SMART process to repair leaks
It is common to have a disassociation between desired results and the interpretation of cascaded actions executed in industrial facilities. For example, most facilities want to save money by eliminating or minimizing the energy consumption associated with compressed air leaks. In order to achieve this goal, most facilities will invest in an ultrasonic leak detection tool maintenance personnel can use to locate and tag compressed air leaks.
Some organizations will contract an outside service organization to perform a leak survey to identify and tag all of the leaks. However, placing a tag on a leak has no impact on the monthly utility bill. Energy savings cannot be realized until field-level actions are aligned with the desired results. In this situation, finding all of the leaks becomes the interpreted objective, with leak repair an assumed result. It is important to note that identified leaks must be converted to a reduction in compressed air demand with a measurable decrease in compressor supply energy to produce energy savings.
Industrial facilities should employ the SMART planning process to achieve energy conservation from compressed air leaks. SMART is an acronym used by many organizations to create objectives with a high probability of success. A SMART objective should be:
Whether the intention is to develop an ongoing leak management program or attack leaks as a specific project, incorporating these SMART attributes will help ensure efforts are converted into desired results.